This paper argues that Aristotelian thumos is a non-reducible mental phenomenon that plays a central role in Aristotle’s theory of the mind, motivation, and action. For Aristotle, thumos is not primarily, as others have argued, a desire for the noble, social appraisal, or retaliation; rather, it is an inner drive or impulse to act. More precisely, it is an executory urge to implement or enact one’s ends or goals, whatever they are. Thumos accounts for someone’s proneness to spring into action (...) and can contribute to bringing about rational or non-rational, first-order desires. It is a second-order motivation, which both human and non-human animals have and that comes in degrees: we can be more or less thumotic, which amounts to being more or less disposed to making first-order desires effective so that they issue in actions. Aristotelian thumos, then, anticipates features of the modern notion of the will. Along the way, I argue that thumos is key to Aristotle’s efforts to differentiate and hierarchically organize species, characters, genders, and peoples. (shrink)